[ExI] Coal gas [Re: Somewhat off topic]

Keith Henson hkeithhenson at gmail.com
Mon Oct 9 18:52:04 UTC 2023

This proposal is an attempt to deal with the economics of intermittent
renewables.  The problem with making hydrogen from PV is the cost of
the platinum in the electrolysis cell and the fact that they run only
~1/3rd of the time, increasing the capital cost (already high) by a
factor of 3.

Without actually having the numbers, I *think* the cost of a submerged
arc system would be much less than platinum cells per unit of hydrogen
produced.  These have never been designed and built and I can see
serious problems with thermal cycling.

But if the problems can be solved, this is a way to make use of
intermittent power and produce an energy-rich storable product.

Open to other ideas.


On Mon, Oct 9, 2023 at 10:40 AM Geoffrey Landis
<geoffrey.landis at gmail.com> wrote:
> Yes, that's "coal gas" (or town gas), a process used for gas lights and ovens before we had long-distance natural gas pipelines that delivered natural gas that was abundant as a byproduct of petroleum drilling. (That's why in early 20th century novels you see people committing suicide by sticking their heads in a gas oven without lighting it. Town gas was very poisonous. Natural gas isn't, so nobody commits suicide that way now.).
> <p>Not a good way to store renewable energy, though; since as you point out, most of the energy is from the coal, not the added heat. Unless your process is more than 80% energy efficient, it takes more renewable energy to make it than you get back.
> On Sunday, October 8, 2023 at 10:24:25 PM UTC-4 hkeith... at gmail.com wrote:
>> But not much worse than moving the ISS to a better storage orbit.
>> H2O + C → H2 + CO (ΔH = +131 kJ/mol)
>> The reaction is endothermic, so the fuel must be continually re-heated
>> to maintain the reaction. (Wikipedia)
>> Carbon is 12 gm/mol. 83 mol/kg and a kg would soak up 10900 kJ. A
>> metric ton of carbon evaporated in steam would need 10900000 kJ or
>> 3.03 MW hours.
>> This would produce 1/6th of a ton of hydrogen with a combustion energy
>> content of 50 MWh/ton, about 8.3 MWh. CO combustion is 10.1 MJ/kg. We
>> have 2800 kg or about 7.85 MWh. So we make about 16 MWh of gas from a
>> ton of coal and 3 MWh of renewable electric power. Most of the energy
>> in the gas is from the coal.
>> It’s an interesting way to use intermittent power though. From this
>> point, the gas can be stored for winter, burned in combustion
>> turbines, or made into methane or diesel.
>> To solve the CO2 buildup we would still need to do air capture, but
>> that has to be done anyway.
>> Keith
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